Known in the prior art are living virus culture vaccines used for prophylaxis of canine distemper. The vaccines contain attenuated strains of distemper viruses adapted to cell cultures of dog or monkey kidneys, or chick embryos.
The "Rockborn" vaccine comprising an attenuated strain of the canine distemper virus, obtained from a wild strain, isolated from the blood of a dog affected with distemper, is prepared on a dog kidney culture cell. To prepare the vaccine, said strain is adapted to the dog kidney cell culture by over 50 passages, and cultivated on said cell culture in a Hanks' solution containing 0.5 percent of lactalbumin hydrolysate and 10 percent of horse serum, or 20 percent of calf serum, or on Earle's medium containing 0.5 percent of lactalbumin hydrolysate and 2 percent of horse or calf serum. The temperature of adaptation is maintained at 30.degree.-37.degree. C., preferably at 35.degree.-37.degree. C. The obtained vaccine is then stabilized and lyophilized (see U.S. Pat. No. 3,098,011).
Known in the prior art is also a vaccine against canine distemper prepared by ten passages of the virus on a cell culture of dog kidneys in the Earle's medium containing 5 percent of lactalbumin hydrolysate and 5 percent of horse serum at a temperature of 38.5.degree. C. (U.S. Pat. No. 3,354,038).
Said vaccines have high immunogenic activity but there are also some disadvantages inherent in them, one of which is low reproducibility of the virus in the dog kidney cell culture.
Another disadvantage of said vaccines is that dog kidney cell culture is used as the substrate for attenuation of the virus and production of vaccines, but dog kidneys can be contaminated with some other viruses, and a special vivarium is required to keep the dogs away from uncontrollable infection. This envolves extra expenditures.
Still another disadvantage of the vaccines is that it is difficult to determine their biological activity, since the virus reproduction is associated with an indistinctly manifest cytopathogenic action that shows by the 20th day following the infection when nonspecific degenerative changes in the cell can develop and interfere with the assessment of the result.
Still another disadvantage inherent in the known vaccines prepared on the dog kidney cell culture is the slow growth of the cells (a monolayer of cells is only formed by the 5th to 7th day) and this prolongs the process of preparing the vaccine.
Viral vaccines intended to control canine distemper animals obtained by cultivating the virus strain on a 9-day chick embryo cell culture or on chorioallantoic membranes of chick embryo can present danger because of the high contamination of chick embryo with some other viruses, and with viruses of the leukemia-sarcomatous group in particular (see U.S. Pat. Nos. 2,912,361 and 2,965,544).
A vaccine prepared on the chick embryo cell culture from the strain known in the USSR as KF-668 has the same disadvantage.
The American vaccine ASL is harmless and devoid of said disadvantage because it is prepared in the cell culture of chick embryos not affected by leukemia, but special farms are required where such leukemia-free poultry can be raised, which, involves additional expenditures. Moreover, the vaccinal strain of the virus does not produce regular cytopathic action in the chick embryo cell culture which complicates the process of the vaccine production.
Known in the prior art is also a viral vaccine against canine distemper prepared by cultivating the virus of canine distemper on the cell culture of kidneys of green monkeys (cf. U.S. Pat. No. 4,004,974). This vaccine is sufficiently immunogenic, areactogenic, highly standard, and harmless. However, monkey hunting becomes now a difficult problem because of the reduction of their populations. The manufacture of this vaccine is based on the utilization of the waste of poliomyelitis vaccine production and is thus closely connected with this process. It is easy to understand that the construction of an independent facility for the manufacture of the distemper vaccine based on the cell culture of monkey kidneys will be very expensive.
The selection of the cell substrate for the manufacture of the viral vaccine thus seems difficult. The imperative prerequisite is the absence of contamination of the cell substrate with extraneous viruses and also production of the vaccine virus in sufficient amounts.